A conventional drill bit assembly used in downhole directional drilling applications typically comprises a matrix head and a mating pin body. In one type of drill bit assembly, the bit head is a one-piece structure typically made of tungsten carbide. In some drill bit assemblies, a locking ring is provided which mechanically fastens to the matrix head, and which can be welded to the pin body to ensure a secure connection between matrix head and pin body. In another type of drill bit assembly, the matrix head is made of two materials, namely a tungsten carbide crown which is brazed onto a steel pin.
A typical matrix head has a female threaded bore that extends partway into the matrix head, and mates with a male threaded pin end of the pin body. Prior to making up these two parts, a steel polymer material such as Megasteel™ is applied to the threads to provide sealing as well as to add strength to the connection.
When making up the pin body to the matrix head, a predetermined amount of torque is applied to the two parts by a make-up machine. Due to the geometry of the threads, there is no method of precisely achieving a specific rotational alignment between the pin body and the matrix head during the make-up procedure. Therefore, it is difficult to provide features in the matrix head or pin that need to communicate or connect with features in the other of the matrix head, when such communication or connection requires precise alignment of the matrix head and pin body.
For drill bit assemblies that use a locking ring, the locking ring is typically locked mechanically to the matrix head by inserting keys in the matrix head into matching keyholes in the locking ring. After the matrix head and pin body are made up, the locking ring is located in proximity to the pin body such that a weld can be applied around the circumference of the locking ring and the pin body to secure these two parts together. The weld ensures that no relative rotation between the pin body and the matrix will occur during drilling. While the weld is effective to prevent relative rotation, applying an effective weld requires care, skill and time, thereby adding to the complexity and cost of the matrix head assembly process.